1. Field of the Invention
The present invention relates to a method and apparatus for controlling the laser of an optical storage apparatus, and more particularly to a method and apparatus for changing a power level of a laser beam in an optical storage apparatus for various types of optical media including a CD-ROM (compact disk read only memory), a CD-R (compact disk recordable), a CD-RW (compact disk re-writable), and so forth.
2. Description of the Background
Reading and writing techniques for a so-called compact disk (CD) used as an optical mass-storage medium for a computer and the like have been greatly improved in recent years. The a result, three types of the compact disks (CDs), the CD-ROM (compact disk read only memory), the CD-R (compact disk recordable), and the CD-RW (compact disk rewritable), have been developed so far. The CD-ROM is a read only memory type compact disk. The CD-R is a one-time data recordable type compact disk that allows a one-time data writing operation by a user and multiple data reading operations. The CD-RW is a re-writable type compact disk that allows multiple data writing, data reading, and data erasing operations.
A light source is required for the above-mentioned operations. Such as a laser diode, for example, which is relatively compact in size and produces an intense laser beam. The last developed CD-RW uses also the diode laser. However, a technique required to control the power of the laser beam for the CD-RW in different from one for the CD-R. As a result, two different laser beam power controllers may coexist; a first controller for the CD-R that is capable of performing one-time data writing and data reading operations and a second controller for the CD-RW that is capable of performing multiple data writing, reading, and erasing operations.
The CD-R allows one-time data writing and reading operations as mentioned above, but it does not allow a data erasing operation. The data writing and reading operations to the CD-R are performed using the above-mentioned first controller that generates a laser beam that is set at different powers for writing or reading the CD-R. The reading power is generated and supplied continuously when the data of the CD-R is read. However, for the one-time writing operation, the first controller is arranged to supply a laser beam that has a two-level power. Specifically, the power is set at a slightly greater level than the writing power in an initial period and the writing power, which is an appropriate level for writing data, in a successive period. Therefore, the laser beam power for the CD-R must be capable of being changed to three levels, the reading power, the writing power, and the initial power for the writing in the order of increasing power.
The operations of writing, reading, and erasing data of the CD-RW are carried out using the above-mentioned second controller that generates a laser beam changeable in three laser power levels to be used for data writing, reading, and erasing, respectively. The reading power is continuously generated and supplied when data of the CD-RW is read, and the erasing power is continuously generated and supplied when data of the CD-RW is erased. However, the data writing operation to the CD-RW requires a different technique.
More specifically, for the data writing operation to the CD-RW, the second controller supplies a laser beam that is set at the erasing power level continuously during a process of writing an area to be written as a blank area, which means no data. And, during a process of writing an area to be written as a pit area, which means an existence of data, the second controller normally supplies the laser beam that is set at the writing power level. To form the pit area in a better way on the CD-RW, the second controller is arranged to supply the laser beam that has a varying power in a form of multiple pulses, each pulse having a value of the writing power as a top peak value and a value of the reading power as a bottom peak value. Therefore, the CD-RW data writing operation also requires three power levels, the reading power, the erasing power, and the writing power in the order of increasing power.
It may be advantageous if the above-described second controller that produces a laser beam variable in three power levels can combine the controls of handling various different types of the optical disks such as the CD-R, the CD-RW, and so forth. However, in this case, a problem will occur on the CD-R during the one-time data writing operation. The problem is that an entire portion of the CD-R will wrongly be written as a pit when the erasing power for the CD-RW is equal to or greater than the one-time writing power for the CD-R. This is because, when the erasing power for the CD-RW is equal to or greater than the one-time writing power for the CD-R, the erasing power for the blank area becomes a writing power and the area to be kept as a blank will be written as data.
As a result, no blank area is made and, thus, the entire portion of the CD-R is wrongly written as a pit. Due to the fact that the erasing power for the CD-RW, which is the second strong power for the CD-RW data writing operation, is necessarily used an the writing power for the CD-R, which is the second strong power for the CD-R data writing operation, the above-described problem is unavoidable.
Because of the above-described problem, the controllers for the CD-R and the CD-RW are not possible to be combined together. Therefore, presently, there is no controller that is capable of handling various types of the optical media such as the CD-R and the CD-RW, for example.